Mould and method for vacuum assisted resin transfer moulding

ABSTRACT

A mould and method for vacuum assisted resin transfer moulding of a fibre reinforced laminated structure are provided. The mould includes a first mould part and a second mould part. The first mould part defines a negative impression of the laminated structure, being structurally stable and forming a support for fibre reinforcement layers of the laminated structure. The second mould part connectable to the first mould part for closing the mould and defines together with the first mould part an enclosed space which can be evacuated. The mould further includes a flow duct for guiding a liquid polymer which is formed as a recess in the first mould part and/or a recess in the second mould part that is open towards the enclosed space and extends along a section of the periphery of the first mould part and/or the second mould part.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of 12/383,959 filed Mar. 31, 2009, whichclaims priority of European Patent Office application No. 08006813.3 EPfiled Apr. 3, 2008. All of the applications are incorporated byreference herein in its entirety.

FIELD OF INVENTION

The present invention relates to a mould for a vacuum assisted resintransfer moulding of a fibre laminated structure, in particular of awind turbine rotor blade, and to a method for vacuum assisted resintransfer moulding.

BACKGROUND OF INVENTION

Vacuum assisted resin transfer moulding (VARTM) of large structures hasto date involved in the inclusion of conduits for resin distributioninto the moulded structure. Examples therefore are disclosed in EP 1 310351 B1, WO 2006/058540 A1, WO 2006/058541 A1, and WO 2007/038930 A1.

EP 1 310 351 B1 describes a mould for wind turbine rotor blades whichcomprises a lower mould part, an upper mould part, and a core. Forforming a laminated rotor blade, fibre reinforcement layers are layeredin the lower mould part and the core is put atop on the layers. Layersections projecting over the lower mould are then wound around the coreso as to overlap in the middle of the core and then the upper mould partis set atop on these layers. When the leading edge of the layer stack isformed a flow pipe is integrated into the stack of fibre reinforcementlayers so as to allow for distributing resin to the layers. This flowpipe will be part of the laminated wind turbine rotor blade after curingthe resin. semi-permeable membrane. In this method, a mould is appliedwith a mould cavity, in which a fibre insertion is placed whichcomprises a plurality of fibre layers and a distribution layer. Thedistribution layer allows for a higher rate of flow for a liquid polymerthan the fibre layers. Inlet channels are located atop of the fibreinsertion. The liquid polymer is directed via the inlet channels to thedistribution layer after the mould has been closed by use of a vacuumbag.

WO 2006/058541 A1 describes a method and an apparatus for producingfibre composite mouldings by means of vacuum infusion. In the method, amould with a mould cavity, a plurality of inlet channels communicatingwith the mould cavity, and a polymer source with liquid polymer isapplied. A plurality of vacuum channels communicates with the mouldcavity and a vacuum source. Fibre material is inserted into the mouldcavity prior to the process of filling said mould, and where a reducedpressure is generated in the vacuum channels and thus in the mouldcavity with the result that liquid polymer is drawn from the polymersource via the inlet channels into the mould cavity. One or more of theinlet channels can also communicate with the vacuum source and/or one ormore of the vacuum channels can also communicate with a polymer source.

WO 2007/038930 A1 describes a method for producing a fibre reinforcedproduct. In the method, one or more layers of reinforcing fibres areplaced into the cavity of a mould. The layers are covered with a resindistribution member over which a number of resin inlets which are formedby pipes are placed. The resin distribution member can be removed afterproducing the laminate. Alternatively, the resin distribution member andthe inlets can remain part of the laminate. If the resin distributionsystem, i.e. the inlet pipes and/or the resin distribution layer,remains in the laminated structure, it adds to weight without providinga substantial structural benefit. On the other hand, if the resindistribution layer is removed from the laminated structure, this is anelaborate process since the distribution layer is provided on a largefraction of the finished structure's surface area.

SUMMARY OF INVENTION

It is therefore a first objective of the present invention to provide anadvantageous means for producing fibre reinforced laminated structures.It is a second objective of the present invention to provide anadvantageous method for vacuum assisted resin transfer moulding of afibre reinforced laminated structure

The first objective is solved by a mould for vacuum assisted resintransfer moulding of a fibre reinforced laminated structure. The secondobjective is solved by a method for vacuum assisted resin transfermoulding. The depending claims contain further developments of theinvention.

According to the invention, a mould for vacuum assisted resin transfermoulding of a fibre reinforced laminated structure is provided. Themould comprises at least a first mould part and a second mould partwhere the first mould part defines a negative impression of thelaminated structure, is structurally stable, and forms a support forfibre reinforcement layers of the laminated structure. The second mouldpart is connectable to the first mould part for closing the mould anddefining together with the first mould part an enclosed space which canbe evacuated. According to the invention, at least one flow duct forguiding a liquid polymer is formed as a recess in the first mould partand/or in the second mould part. The recess is open towards the enclosedspace and extends along a section of the periphery of the first mouldpart and/or the second mould part.

In the inventive mould, the flow duct is located outside the actualvolume of the finished fibre reinforced laminate structure but is partof the volume which will be evacuated. When forming the fibre reinforcedlaminated structure the flow duct is kept free of any material until theinjection of resin starts. Thus, when the injection of the resin isstarted, the resin can run freely through the flow duct from an inletport through which the flow duct is connected to a resin reservoir. Asthe flow duct is filled with resin, the slower process of resin flowinginto the fibre and core materials of the laminated structure starts.Once the resin has cured and the mould has been removed the surplusresin which is the reminder of the resin in the flow duct can be removedby mechanical means. By using a flow duct which is part of the mouldrather than of the moulded structure lay-up time for the layer stack,weight, costs and complexity of the laminated structure can be reduced.

The first mould part can, in particular, define the negative impressionof a laminated structure having an elongated shape with a leading edgeand a trailing edge. In this case, a first flow duct may be present inthe first mould part and/or in the second mould part at a location wherethe leading edge is to be fowled. Furthermore, a second flow duct may bepresent in the first mould part and/or in the second mould part at alocation where the trailing edge is to be formed. The first and secondflow ducts allow for introducing resin from the leading edge, as well asfrom the trailing edge into the fibre- and core materials of the layerstack in the mould. The use of the first and second flow ducts allow forreducing the infusion time making the use of cheaper, faster settingresins possible. The flow front is then essentially a combination of twomore or less straight lines, parallel to the leading edge and thetrailing edge, respectively. In combination with non-parallel leadingand trailing edges this ensures that the flow fronts coalesce in asystematic, controlled manner, thereby minimising the risk of entrappingair.

The laminated structure with the elongated shape can, in particular, bea laminated wind turbine rotor blade.

In a first implementation of the inventive mould the second mould partis also structurally stable. This helps to prevent wrinkles in thefinished laminated structure. Moreover, in this implementation a firstrecess can be formed in the first mould part while a second recess isformed in the second mould part. The first recess and the second recessare then located such in the respective first and second mould partsthat parts of their open sides are aligned to each other when the mouldis closed. In other words, when the mould is closed the first recess andthe second recess together faun the flow duct for the liquid polymer tobe introduced into the stack of fibre- and core materials.

Like the first mould part, the second mould part can also define anegative impression of the laminated structure. Then, a mould core ispresent in addition to the first and second mould parts. The outerdimensions of the mould core are smaller than the inner dimensions ofthe first and second mould parts. The mould core may optionally besurrounded by an inflatable member. By using first and second mouldparts which both define negative impressions of the laminated structureand the mould core, a whole closed structure can be formed in onemoulding process. For example, if a wind turbine rotor blade is to beformed as the laminated structure the whole shell of the rotor blade canbe formed in one moulding process. This overcomes the necessity of gluejoints at the trailing edge and the leading edge of the rotor bladesince the fibre layers can be dimensioned such that they can be woundaround the core so as to overlap, for example, in the centre of theupper mould part. When forming the laminated structure the inflatablemember can be used to press the stack of reinforcement- and core layerson the first and second mould parts. Inflating the inflatable member canbe automatically done by evacuating the space between the first andsecond mould parts on the one side and the core on the other side. Ifthe inflatable member has an internal pressure or a flow connection toair pressure reservoir, e.g. inside the mould core, the inflation willbe self-affected by evacuating the space between the core and the firstand second mould parts.

In a second implementation of the inventive mould the second mould partis a vacuum bag. In this case, the at least one flow duct is formed as arecess in the first mould part. By using a vacuum bag a mould corebecomes unnecessary so that the number of mould parts can be reduced ascompared to the first implementation. However, forming a laminatedstructure in which both ends of the fibre- and core layers of the layerstack overlap so as to form, e.g., a closed shell of a wind turbinerotor blade, is not possible so that glue joints will be necessary.

The inventive method for vacuum assisted resin transfer moulding of afibre reinforced laminated structure uses an inventive mould. In themethod, the at least one flow duct is kept free of any material untilthe resin is injected by injection means. The resin then runs in the atleast one flow duct from an inlet port to the far end of the mould. Whenthe resin has set, the mould parts are removed and the surplus resin inthe at least one flow duct may be removed mechanically.

If at least two flow ducts are present, a resin reservoir may beconnected to the at least two flow ducts in such a way that the resin isinjected into the at least two flow ducts simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, properties and advantages of the present inventionwill become clear from the following description of embodiments inconjunction with the accompanying drawings.

FIG. 1 shows a first embodiment of the inventive mould.

FIG. 2 shows a detail of FIG. 1

FIG. 3 shows the detail of FIG. 2 in a top view

FIG. 4 shows a second embodiment of the inventive mould.

FIGS. 5 to 9 show a third embodiment of the inventive mould and its usefor making a fibre reinforced laminated wind turbine rotor blade.

DETAILED DESCRIPTION OF INVENTION

The first embodiment of the inventive mould is shown in FIG. 1. Thefigure shows a mould for a shell part of a fibre reinforced laminatewind turbine rotor blade. The shell part to be formed by the mould formsthe pressure side of the later rotor blade, i.e. the side which showssubstantially towards the direction from which the wind comes duringoperation of the wind turbine. A similar mould (not shown) will be usedfor forming the suction side shell part. The wind turbine rotor blade isthen formed by joining the pressure side shell and the suction sideshell by glue joints.

The mould 1 shown in FIG. 1 comprises a first mould part 2 which is madefrom a rigid and structurally stable material. The mould part 2comprises an inner surface 4 which defines a negative impression of thewind turbine rotor blade's pressure side shell part. The surface 4 ofthe mould part 2 may be provided with a suitable release agent whichallows for removing the pressure side shell part from the mould afterthe moulding process.

The mould 1 further comprises a vacuum bag 6 which may be fixed in apressure tight manner to edges 8, 10 of the mould part 2. The vacuum bag6 and the mould part 2 together define an enclosed space which can beevacuated through suitably placed vacuum channels (not shown in thefigure).

The rigid mould part 2 is equipped with recesses 14, 16 which form flowducts after evacuating the enclosed space. The flow ducts 14, 16 can beprovided with spacer elements 18 which prevent the vacuum bag 6 frombeing sucked into the flow ducts 14, 16. The spacer elements 18 can beseen in FIGS. 2 and 3 which show an enlarged view of the flow duct 14 ina sectional view and in a top view, respectively.

For vacuum assisted resin transfer moulding of a wind turbine rotorblade as a fibre reinforced laminated structure a layer stack 12 is laidin the mould part 2. Then, the vacuum bag 6, which constitutes a secondmould part in the present embodiment, is fixed airtight to the edges 8,10 of the mould part 2, and the enclosed space between the mould part 2and the vacuum bag 6 is evacuated. This leads to pressing the vacuum bag6 against the layer stack 12 by means of the air pressure outside of themould 1. Then, a liquid polymer is introduced into the flow ducts formedby the recesses 14, 16 from where it flows into the layer stack 12. Thereservoir of the liquid polymer is connected to both flow ducts so thatit can be injected into both flow ducts 14, 16, simultaneously. As theflow ducts become filled with the liquid polymer, the slower process ofliquid polymer flowing into the layer stack 12 starts. The flow front ofthe resin is essentially a combination of two more or less straightlines, which run parallel to the leading and trailing edge of the shellpart to be formed. When combined with non-parallel leading and trailingedges, this ensures that the flow front coalesce in a symmetric,controlled manner, thereby minimising the risk of entrapment of air.

When the layer stack 12 is fully wetted by the liquid polymer the liquidpolymer is cured, for example by using heat or ultraviolet light. In thepresent case, heat is used which is applied by a heat transfer system 20that may, e.g., be realised by heating filaments integrated into themould part 2. After the resin is cured the mould will be removed againleaving surplus liquid polymer at the leading and trailing edges of theshell part. This surplus polymer is then removed by mechanical means.

The layer stack in the present embodiment can comprise one or morelayers of fibre reinforced material onto which a core material isprovided which may be made, e.g., from balsa wood or PVC foam.

Although the mould part 2 in FIG. 1 is realised as a single mouldelement it may as well be realised by a number of mould elements whichare joined together to form the mould part 2.

A second embodiment of the inventive mould will be described withrespect to FIG. 4. The mould 21 comprises a first mould part 2 and asecond mould part 22 which are both made from a structurally stable,rigid material. The first mould part 2 substantially corresponds to themould part 2 of the first embodiment and will therefore not be describedagain. Moreover, the elements of the first mould part 2 as well as thelayer stack 12 shown in FIG. 4 are designated with the same referencenumerals as in FIG. 1.

The second embodiment differs from the first embodiment in that a secondstructurally stable, rigid mould part 22 is used instead of a vacuum bag6 for closing the mould to form an enclosed space which can beevacuated. The second mould part 22 comprises a surface 23 that definesa positive impression of the wind turbine rotor blade's pressure sideshell and edges 24, 26 which allow for joining the first mould part 2and the second mould part 22 airtight so that an enclosed space isformed between both mould parts. Like the surface 4 of the first mouldpart 2 the surface 23 of the second mould part 22 may be provided with asuitable release agent for simplifying dismantling the finished shellpart from the mould. The second mould part 22 further comprises a firstrecess 28 and a second recess 30 which are dimensioned and located suchin the second mould part 22 that open sides of them are aligned with therecesses 14, 16 of the first mould part 2 so as to form flow ducts forthe liquid polymer. Furthermore, the second mould part 22 is equippedwith one or more suitably located vacuum pipes 32 for evacuating theenclosed space between the first and second mould parts 2, 22.

The process of vacuum assisted resin transfer moulding of the shell partis substantially the same as in the first embodiment and will thereforenot be described again.

A third embodiment of the inventive mould and its use will be describedwith respect to FIGS. 5 to 9.

FIG. 5 shows a first mould part of the mould 101 according to the thirdembodiment which corresponds to the first mould parts of the first andsecond embodiments except for the fact that no recess 16 is present inthe mould part's edge 110 that is located where the wind turbine rotorblade's trailing edge will be formed. The remaining parts of the firstmould part 102 of the third embodiment correspond to the respectiveparts of the mould part 2 of the first and second embodiments and willtherefore not be described again. Elements of the mould part 102 whichcorrespond to the mould part 2 are designated with the referencenumerals which are increased by 100 with respect to those used for themould part 2.

A layer stack 112 is formed in the first mould part 102 (see FIG. 6) byfirst putting one or more layers of fibre reinforcement material in themould, then putting a core material atop of these layers and then againone or more layers of fibre reinforcement material atop of the corematerial. The layers of fibre reinforcement material are dimensionedsuch that their end sections 122, 124 project over the edges 108, 110 ofthe mould part 102. At the edge 110 where the trailing edge of the windturbine rotor blade is to be formed, a special core part 126 is put atopof the layers of fibre reinforcement material. To aid distribution ofthe liquid polymer during the moulding process, the layer stack may beequipped with transfer passages 128, 130 extending through the layerstack.

In the next step, as it is shown in FIG. 7, a mould core 132 is set ontothe layer stack 112. In the present embodiment, the mould core 132consists of a first and a second mould core part 134, 136 between whicha shear web 138 is located. The shear web may consist of a layer stackwith the same layer structure than the layer stack 112 in the firstmould part 102. During the vacuum assisted resin transfer mouldingprocess the shear web will be firmly joined to the shell of the windturbine rotor blade to increase its stability. Although only one shearweb 138 is present in the shown embodiment, two or more shear webs couldbe present as well.

The mould core parts 134, 136 are made from a structurally stablematerial like, for example, wood. Moreover, the structurally stablematerial may be surrounded by a flexible member like, for example, foamrubber. In addition, each core part 134, 136 is surrounded by a flexiblemembrane the outer surface of which may be treated with a suitablerelease agent. When the space between the mould parts and the mould corewill be evacuated after closing the mould, the air pressure stillpresent between the structurally stable material of the mould core parts134, 136 and the flexible membrane will lead to an inflation of themembrane so that the layer stack surrounding the mould core parts 134,136 is pressed against the respective mould parts.

In a next step, as it is shown in FIG. 8, the top fibre reinforcementlayers, i.e. those layers atop of the core material of the layer stack112, are wound around the mould core 128 such that both ends of thelayers overlap. Then, a core material is put atop of these layers andthen the lower fibre reinforcement layers of the layer stack 112, i.e.those which are below the core material of this stack, are wound aroundthe core material to form a layer stack 140, thereby overlapping intheir end sections. In this way the whole shell of a wind turbine rotorblade can be made in form of a single laminate structure without theneed of glue joints at the leading and trailing edges of the rotorblade.

In a last step, as it is shown in FIG. 9, the second mould part 142 ofthe mould 101 is set atop of the layer stack 140. The second mould part142 comprises edges 144, 146 by which the second mould part 142 can bejoined airtight with the first mould part 102. Suitable vacuum channels(not shown) can be used for evacuating the space enclosed between themould parts 102, 142. The second mould part further comprises a firstrecess 148 and a second recess 150. The location of the first recess 148and its dimension are chosen such that an open side of the recess 148 isaligned with an open side of the recess 114 in the first mould part 102when both mould parts are joined together. Hence, the recess 114 in thefirst mould part 102 and the recess 148 in the second mould part 142form together a flow duct for liquid polymer at the leading edge of thewind turbine rotor blade to be formed which is open towards the spaceenclosed between the mould parts. In addition, the recess 150 in thesecond mould part 142 forms a further flow duct for liquid polymer whichis located at the trailing edge of the wind turbine rotor blade to beformed.

After evacuating the enclosed space between the mould parts 102, 142 aliquid polymer is injected into the flow ducts which then flows into thelayer stacks 112, 140 and the shear web 138. When the layer stacks 112,140 and the shear web 138 are completely wetted by the liquid polymer,the liquid polymer is cured by applying heat via heat transfer systems120, 152 present in the first and second mould parts 102, 142. Like inthe other embodiments, the heat transfer system may be realised in formof heating filaments integrated into the mould parts 102, 142. When theliquid polymer is cured the mould parts 102, 142 and the mould coreparts 134, 136 are removed. After removing the mould from the windturbine rotor blade surplus polymer material remains at the leading edgeand the trailing edge of the wind turbine rotor blade. This surpluspolymer material is then removed mechanically.

The inventive mould allows for forming fibre reinforced laminatedstructures by using a vacuum assisted resin transfer moulding processwithout leaving flow pipes in the finished structure. Moreover, removingthe surplus resin material is easier and less elaborate than removingflow pipes used in the state of the art moulding processes.

1. A method for vacuum assisted resin transfer moulding of a fibrereinforced laminated structure, comprising: providing a for vacuumassisted resin transfer moulding of a fibre reinforced laminatedstructure, comprising: a first mould part defines a negative impressionof the fibre reinforced laminated structure, the first mould partstructurally stable and forms a support for fibre reinforcement layersof the fibre reinforced laminated structure, a second mould partconnectable to the first mould part in order to close the mould andtogether with the first mould part defines an enclosed space to beevacuated, a flow duct that guides a liquid polymer, the flow duct isopen towards the enclosed space and is formed as a recess in the firstmould part extending along a section of a periphery of the first mouldpart and/or a formed as a recess in the second mould part and extendingalong a section of the periphery of the first mould part; and a spacerelement forming a portion of the flow duct, the spacer elementconfigured to prevent the second mould part from entering the flow ductafter the enclosed space has been evacuated, keeping the flow duct freeof any material until the resin is injected; and injecting the resinsuch that the resin runs in the flow duct from an inlet port to a farend of the mould.
 2. The method as claimed in claim 1, wherein the mouldincludes a plurality of flow ducts, and wherein a resin reservoir isconnected to the flow duct such that the resin is injected into theplurality of flow ducts simultaneously.
 3. The method as claimed inclaim 1, further comprising: removing the mould parts when the resin hasset; and mechanically removing the surplus resin in the flow duct. 4.The method as claimed in claim 1, wherein the fibre reinforced laminatedstructure is a laminated wind turbine rotor blade.